Hierarchy of vibrational state sets for the solution of the CO2 non-LTE problem

The extended non-LTE model for the CO2 infrared bands in the Earth atmosphe re includes a set of 328 vibrational states of seven CO2 isotopes (Shved et al., 1998). To simplify solving the non-LTE problem of radiative transfer in the CO2 bands, a procedure of reducing the amount of the vibrational sta tes is formulated. A hierarchy of three models, which are simplier than the extended model but provide a reliable accuracy of estimating non-equilibri um populations, is proposed. In the direction of decreasing accuracy, these simplified models include 206 and 117 states of seven CO2 isotopes, and 60 states of five CO2 isotopes, respectively. Even the simplest model allows evaluation the populations of the lower vibrational states with a reasonabl e precision. The errors in estimating the total non-LTE limb radiance for t he 4.3 and 15 mu m CO2 bands with this model do not exceed the order of 10% and 1%, respectively, Use of the simplest model in evaluating the rate of net radiative heating in all the infrared CO2 bands gives errors which do n ot exceed similar to 0.01 K/day above about 80 km and increase down to the stratopause up to similar to 0.04 K/day. (C) 2000 Elsevier Science Ltd. All rights reserved.